This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This research aims to further our understanding of the neurobiological mechanisms underlying social support in the context of friendship. Countless studies have identified social support as critical in protecting individuals from the deleterious mental and physical health consequences of both acute and chronic stressors (Uchino et al., 1996), yet the underlying neurobiological mechanisms remain unclear. The importance of examining the specific mechanisms underlying friendship is underlined by the fact that friends are vital for the healthy psychosocial adjustment of children (Erath et al., 2010), and an understanding of the mechanisms by which friends act as social buffers to immature individuals may explain why more socially isolated youngsters are at greater risk for developing mental and physical illnesses later in life (Bagwell et al., 1998). This project has three specific goals: 1) To identify brain areas involved in juvenile rhesus monkey (Macaca mulatta) friendships using non-invasive imaging techniques (i.e. positron emission tomography);2) To determine the effectiveness of a friend versus a familiar companion in reducing brain activity in regions known to mediate stress and anxiety;3) To examine the associations between behavior, brain activity, and central and peripheral levels of oxytocin, vasopressin, and cortisol within the context of friendship. We hypothesize that 1) the neural circuitry of friendship shares in common many of the pathways that have been implicated in attachment relationships;2) the presence of a friend during exposure to a psychosocial stressor, as compared with the presence of a familiar peer, will be associated with reduced activity in limbic structures typically involved in responding to threatening experiences, which will in turn reduce cortisol levels;and 3) the presence of a friend during exposure to a psychosocial stressor, as compared with the presence of a familiar peer, will be associated with increased affiliation, which will activate central oxytocin- and vasopressin-releasing neurons and result in higher levels of these neuropeptides in cerebrospinal fluid and plasma.